Display racks, cabinets, etc., used in general exhibition halls or in temporary displaying or selling places are mostly temporary works. Therefore, besides their innovative and beautiful external appearance, the most important feature of temporary racks, cabinets, etc., is that they shall be easy to install and to dismantle, so as to facilitate the construction and to minimize the construction time. Special exhibition or display sites sometimes call for long lengths or pipes, which are not possible to be prefabricated and stored in advance (because it occupies more space and has less usage). Therefore, these special length pipes are ordered on a demand basis. However, since the quantity ordered is small, the cost is relatively high, and in most cases, the order is impossible to fulfill. However, even though there are quite a lot of fitting types available on the market, their construction is not very different and, further, their assembly is rather time consuming. Also, they are not flexible enough in their applications or usages.